The present invention relates to a power supply apparatus for a vehicle telephone, a vehicle facsimile and the like.
Japanese Laid Open Patent Publication 62-74455 discloses a power supply apparatus for a vehicle. The conventional power supply apparatus comprises a battery for supplying electric power to vehicle equipment, a capacity detector for detecting remaining capacity of the battery, a switching member for turning off the power supplied from the battery to the vehicle equipment and a control unit for controlling the switching member while the capacity of the battery is below a certain level. According to the conventional apparatus, the battery is protected from excessive discharge.
However, it is very hard to detect the remaining capacity of the battery accurately. When battery fluid is dense, the remaining capacity of the battery seems to be higher than the actual capacity. Contrary to this, when the battery fluid is thin, the remaining capacity of the battery seems to be lower than the actual capacity. Thus, the remaining capacity of the battery is sometimes erroneously detected and the battery may be excessively discharged.
A vehicle has an engine starter which requires a huge amount of electric power. When the remaining capacity of the battery is low, the engine starter cannot start the engine quickly.